In order to synchronize generation assets for electrical grid operation, the alternating current (ac) frequency must be held within tight tolerance bounds. Different methods available for “frequency regulation” include generator inertia, adding and subtracting generation assets, dedicated demand response and electricity storage. Each of these methods has pros and cons, and the implementation of these methods takes from a millisecond to 20 minutes. In the group of “ancillary services” provided in the open market management of the grid, frequency regulation has the highest value. Frequency regulation is mainly provided by ramping (up and/or down) of generation assets. This typically takes minutes rather than seconds. Electricity storage has the capability for doing the job in milliseconds, and Pacific Northwest National Laboratory (PNNL) has suggested millisecond electricity storage should have a value of at least twice that of 20 minute assets.
Numerous reports are available addressing frequency regulation. Early reports come out of U.S. Department of Energy (DOE) national laboratories. Oak Ridge National Laboratory (ORNL) first proposed this be addresses in the early 2000’s. DOE has since sponsored investigations and reports including ones from PNNL, Sandia National Laboratories (SNL), Idaho National Laboratory (INL) and Lawrence Berkeley National Laboratory (LBL).
Below are two charts from the report: Use of Frequency Response Metrics to Assess the Planning and Operating Requirements for Reliable Integration of Variable Renewable Generation Joseph H. Eto, Principal Investigator Lawrence Berkeley National Laboratory, 2010.
By nature, frequency regulation is a “power storage” application of electricity storage. It has been identified as one of the best “values” for increasing grid stability and is not considered “an energy arbitrage” play such as storing wind energy at night for day use. It typically costs between $10 and $60 per megawatt hour.